Small bulk helically wound antennae and method for making same

ABSTRACT

Small bulk cylindrical or conical antennae made of a helically wound conductor with a free end and a grounded end. The coupling to a power supply or a load circuit is effected along a short length of said conductor near to and terminating on said ground plane, either by direct shunt coupling or by inductive coupling. The grounded end can be provided with a capacitive load. The antennae can be manufactured by sticking a metal strip to a dielectric sheet and rolling the latter to the desired shape, or by printing circuit technique and subsequent winding to said shape, in which they may be kept by clamping, glueing or any other method.

United States Patent Inventors 7 Roger L. Gouillou Draveil; Guy F.Ringenbach, Villeneuve-le-Roy;

Jacques H. Delomini, Epinay-sur-Seinc,

[56] References Cited UNITED STATES PATENTS 2,l74,353 9/1939 Roberts343/895X 2,495,399 1/1950 Wheeler 343/895X 3,449,752 6/1969 Spitz et al.343/895 OTHER REFERENCES France AppL No. 782,337 Filed Dec. 9, 1968Patented Apr. 6, 1971 Assignee Office National DEtudes Et De RecherchesAerospatiales Chatillion-Sous-Bagneux, France Priority Dec. 15, 1967,Feb. 26, 1968 France 132,155 and 141,294

SMALL BULK HELICALLY WOUND ANTENNAE AND METHOD FOR MAKING SAME 9 Claims,19 Drawing Figs.

us. Cl. 343/895, 343/745, 343/843 1m. (:1 l-l0lq l/36 Field ofSearch343/895, 745,843

Helical Beam Antenna by John D. Kraus Communications for September 1949,pages 6- 8 and 34 relied upon, 343- 895 Primary Examiner-Herman KarlSaalbach Assistant Examiner-Saxficld Chatmon, Jr Attorney-Abraham A.Saffitz ABSTRACT: Small bulk cylindrical or conical antennae made of ahelically wound conductor with a free end and a grounded end. Thecoupling to a power supply or a load circuit is effected along a shortlength of said conductor near to and terminating on said ground plane,either by direct shunt coupling 7 or by inductive coupling. The groundedend can be provided with a capacitive load. The antennae can bemanufactured by sticking a metal strip to a dielectric sheet and rollingthe latter to the desired shape, or by printing circuit technique andsubsequent winding to said shape, in which they may be kept by clamping,glueing or any other method.

5 Sheets-Sheet 1 INVENTORS:

Roger L. GOUILLOU, Guy F. nmcsmmcn,

Jacques H. DE OMINI 1AM aw AT 0R "Y Patented 7 April 6, 1971 5Sheets-Sheet 2 mvmrous:

Roger L. GOUILLOU, Guy 1-. amcsmmcn,

Jacques H. DELOMINI y flLLZdo M 4 5 Sheets-Sheet 5 Fig.8

INVENTORS:

Roger L. GOUILLOU, Guy F. RINGENBACH, Jacques H. DEL IN I BY Z" ATT NPatented April 6, 1971 3,573,840

5 Sheets-Sheet 4 INVENTORS:

Roger L GOUILLOU Guy F. RINGENBACH, Jacques H. DELO NI ATTO EY PatentedApril 6, 1971 5 Sheets-Sheet 5 INVENTORS UH II mm m LB N UE OGE T GND AM L Ha TF8 e 8 yu Ouq RGCJWW B J SMALL BULK HELICALLY WOUND ANTENNAE ANDMETHOD FOR MAKING SAME The invention relates to antennae for receivingor transmitting ratio-electric signals, more particularly to helicalantennae grounded at one end, the dimensions of the antenna being verysmall, both axially and transversely, with respect to the averageoperating wavelength.

It is important to reduce the size of antennae until they are. verysmall with respect to the operating wavelength, since the antennae canthen be disposed in a restricted space, their weight can be reduced, andtheir mechanical rigidity can be increased. Unless, however, thefacilities according to the invention are used, the reduction in sizeresults in a high negative reactance in the antenna impedance, in serieswith a very low radiation resistance. As a result, it is particularlydifficult to match the impedance to that of a power supply or a loadcircuit; furthermore, the efficiency is low and the frequency pass bandis very narrow.

The aim of the invention is to construct antennae having a singleconductor wound into a cylindrical or conical helix and transmitting awave whose electric field is linearly polarized in a direction parallelto the helix axis, giving a radiation polar diagram which is practicallycircular in a plane perpendicular to the axis, the antennae beingextremely small compared with the operating wavelength in free space,but being capable of having a great varietyof external shapes and thusbeing very easy to adapt to a wide range of operating conditions thoughtheir efficiency is very nearly equal to that of a conventionalhalf-wave dipole, the antennae operating at high efficiency when theyare connected by a coaxial lineto a transmitter or receiver.

According to one method for improving the matching of an antenna with apower supply or a load circuit, the radiating antenna element isassociated with nonradiating elements so as to form a unit resonating atthe operating frequency. It is known, inter alia, to load the top. of avertical antenna from a horizontal conductor, the bottom of the antennabeing grounded.

Other known antennae are caused to radiate a circular polarized wave bywinding the radiating conductor into a helix. As a rule, such helical.antennae are used to transmit or receive signals whose wavelength ismuch smaller than the length of the conductor when unwound, but attemptshave also been made to use them at wavelengths which are equal to orgreater than the unwound length.

Other known helical antennae radiate a wave whose magnetic field ispolarized in a direction perpendicular to the helix axis, with aradiation diagram substantially circular in a plane perpendicular to theaxis, one end of the helically wound conductor being isolated orconnected to a conducting component forming a terminal capacitancewith'respect to ground, whereas the other end is connected to thecentral conductor of a coaxial line whose external conductor isgrounded. These antennae are not very efficient, however, since theirimpedance to the coaxial line is very different fromthe characteristicimpedance of the line.

As a rule, small antennae of the aforementioned type give mediocreresults, either because'the'magnification coefficient of the circuitcontaining them becomes very high with a narrow pass band, or owingtoconsiderable losses, or because the impedance of the antenna at theterminals of the power supply or load is much too small compared withthe impedance of the power supply and'the load themselves.

The present invention provides an antenna comprising a single conductorhelically wound round a geometrical surface having a longitudinal axis,one end of the conductor being connected to a point on a conductiveground plane and the other end being insulated, the antenna comprisingmeans for coupling it to a load circuit and being characterized in that,if )t denotes the wavelengthinfree space corresponding to the operatingfrequency and 1 denotes the total length of the wound conductor measuredalong said conductor, A and satisfy the relation and that the saidcoupling means are coupled to the conductor along a pan of the conductorhaving the said first end as one of its ends, the length of the saidpart being equal to a very small fraction of the wavelength.

The average length of a turn of the helically wound conductor and theaxial length of the antenna both are much smaller that the saidwavelength, and this all the more that there are more turns in thehelical winding. In fact, the said average turn length is equal to thequotient by the number N of the turns of the length l, itself alwayssmaller than 0.45 A

In a first embodiment of the invention, the said coupling means are adirect or shunt connection to the said load circuit between theaforementioned point and another point which is very near to the firstpoint and situated on the conductor.

in a second embodiment of the invention, the said coupling means are amagnetic coupling device comprising a short length of auxiliaryconductor parallel and very near to, but not in contact with, the saidpart of the said antenna conductor, the said length of auxiliaryconductor having one end connected to the said ground plane and theoutput circuit being connected between the ground plane and the otherend of the length of auxiliary conductor.

A number of types of antennae according to the invention will now bedescribed. First, to clarify ideas, the expression extremely small sizecompared with the operating wavelength implies that the diameter of thehelical windings can be as small as one-hundredth of the wavelength infree space, and the axial height can be as small as one-fiftieth of thewavelength. As a result, antennae according to the invention are muchsmaller than prior art antennae.

In the case of a cylindrical helix, experiments by the Applicants haveshown that the height and diameter of the ideal cylinder on which thehelical conductor is wound can be varied within wide limits, providedthat the product of the number of turns N and the diameter d of thecylinder is between one-seventh and one-tenth of the wavelength A infree space at the operating frequency, i.e.:

). llOSNdSh /7 0.l0SNd/)\S 0.14 (1) if the pitch of the helix isconsiderably smaller than the cylinder diameter, the quantity (Nrrd)represents the length I of the antenna wire; in antennae according tothe invention, therefore, the ratio l/A satisfies the condition:

If the helix is conical and not cylindrical, the quantity d should bereplaced by the arithmetical mean of the diameters of the first and lastturn in the helix.

The operation of the antenna and its improved efficiency will now beexplained.

The helical conductor winding greatly reduces the apparent propagationvelocity of electromagnetic energy measured in the direction of thehelix's axis. It is also known that the propagation velocity of theelectromagnetic energy along the conductor itself is slightly less thanit would be if the conductor was rectilinear.

Since the total length of the helically wound conductor is greater, atthe operating frequency, than a quarter of the wavelength in free space,andsince its upper end is insulated whereas its lower end is grounded(or connectedto a ground" conductor plane), the current distributionalong the conductor has maximum intensity at a point near the lower end.Near the end, the local impedance varies very rapidly as the measuringpoint moves along the conductor. If k c denotes the wavelength measuredalong the conductor and x is the distance of the measuring point fromthe lower end, the impedance is expressed by a function of the type Zbeing a very high impedance. The function varies very rapidly in theneighborhood of x=0.

Accordingly, near the lower, grounded end of the antenna, there is adrive point where the apparent impedance, measured between this pointand ground, is close to a predetermined, e.g. the characteristicimpedance of a coaxial supply line.

Furthermore, the above reasoning shows that, allowing for the electricimage with respect to the antenna ground plane, the antenna behavessubstantially like a half-wave antenna, whose favorable properties arewell known.

Furthermore, if the drive point is chosen in the manner described, theimpedance can be transformed so as to transform the aforementionedradiation resistance to a value which facilitates matching with acoaxial supply line.

It is also well known that the maximum power which can be radiated by anantenna energized by a given power supply is independent of the ratio ofits physical dimensions to the wavelength in free space, except to theextent that this ratio makes it difficult to match the supply line to anexcessively small radiation resistance, in which case there would beconsiderable losses through dissipation in the passive resistancesalways present in the system.

Since the device according to the invention performs the aforesaidmatching satisfactorily, it can efficiently transform the energy fromthe power supply into radiant energy.

The invention will be more clearly understood from the followingdescription and accompanying drawings, in which:

FIG. I shows a conically-wound antenna according to the invention, apart of which is shunted by an adjustable capacitor, to facilitatetuning:

FIG. 2 shows an antenna wound around a circular cylindrical surface,according to the invention;

FIG. 3 shows an antenna similar to that of FIG. 1, but without theadjustable capacitor;

FIG. 4 shows an antenna similar to that of FIG. 2, but provided with anadjustable capacitor;

FIG. 5 shows an antenna similar to that of FIG. 2, but coupled in adifferent manner to its load or power supply circuit.

FIGS. 6 and 7 show antennae similar to that of FIG. 2, but provided withan extra capacitive load (hereinafter called roof) at their nongroundedend;

FIGS. 8 and 9 show other forms of cylindrically-wound antennae providedwith a capacitive load having a mechanical shape differing from that ofFIGS. 6 and 7.

FIGS. 10 and 11 illustrate a method for manufacturing acyIindrically-wound antenna by rolling a sheet of insulating material onwhich a conducting strip has been stuck;

FIGS. l2, l3 and 14 illustrate processes for the manufacturing of acylindrically-wound antenna having a capacitive load, by a methodsimilar to that used in the case of FIGS. 10 and 11;

FIGS. 15a, 15b and 16 illustrate a variant of the manufacturing processused in the case of FIGS. 10 and 11; and

FIGS. 17 and 18 illustrate a process for the manufacturing of aconically-wound antenna by rolling a sheet of insulating material onwhich a conducting strip has been stuck or preferably printed.

An example of antenna constructed by the Applicants, which is a specialcase of the class of antennae according to the invention, can bedisposed in a missile head and is shown in FIG. 1. A conductor 41, whoseunwound length is approximately 0.4 )t is wound into a conical helix,the cone containing the central line of the conductor, which has a baseapproximately A /40 in diameter and a height of approximately )t /25.The conductor is driven at point 7, near the grounded end 46, by theinner conductor of coaxial line 43, whose outer conductor 44 isconnected to ground 45. An adjustable capacitor 48 is used for tuning,one plate being connected to point 42 on conductor 41 and the otherplate being connected to ground 45 The antenna has a pass band at 3 db.of attenuation of 3 percent of the operating frequency, and theefficiency is less than 0.5 db. belowthat of a half-wave dipole.

Experiments by the Applicants have shown that the size and shape ofhelical antennae can be varied within very wide limits without affectingtheir optimum performance at wavelengths much greater than theirsizei.e., the antennae can be adapted in the most efficient manner tothe conditions for particular applications, e.g. can be given therequired rigidity and appearance and can be disposed in a requiredspace, etc., provided that the conditions expressed by the relation (1)between the product Nd and the wavelength are precisely adhered to.

FIG. 2 shows a first type of cylindrical antenna according to theinvention.

A silver-coated brass conductor wire 51, 2 mm. in diameter, is rolledinto a helix on a support 52. The support consists of two plates 53, 54perpendicular to one another and made of laminated plastics such asepoxy glass. The two plates form a sort of cylinder, coaxial with theantenna. The cylinder on which the helix is wound is 50 mm. in diameterand 100 mm. high. There are five turns and the length of wire isapproximately cm. The support is fixed on a brass baseplate 55 whichacts as a ground plane and is 2 mm. thick and 70 mm. in diameter.

The antenna is designed to operate at a frequency of 137 MHz., i.e. at awavelength A 2,18 m. It can be seen that The inner conductor of thecoaxial supply line 56 is connected to the antenna wire at a point 57approximately I cm. from the grounded end 59 of the wire. As a result,the distance between the grounded end and the drive point isapproximately one two-hundredths of the wavelength.

The antenna in FIG. 2 is very nearly as efficient as a halfwave dipole,the difference being between 0.5 and I db., and the pass band, of theorder of 1 percent of the average operating frequency, is considerablywider than in prior-art small antennae.

In the variant shown in FIG. 3, the surface containing the central lineof the conductor is not a cylinder but a truncated cone, which flaresout more than in FIG. I. The antenna is as efficient as that shown inFIG. 2, provided that relation (l) is adhered to, where d is thearithmetical mean of the base diameters of the truncated cone. In theantenna shown in FIG. 3, 61 denotes the antenna wire, 65 the earthlevel, 66 the inner conductor of the coaxial supply line, 67 the drivepoint, 68 the coaxial line and 69 the earthed bottom end of the antenna.

Experiments have also shown that helical antennae having a great varietyof shapes (the surface containing the central line of the conductor can,for example, be a truncated cone having elliptic bases) give equallysatisfactory results provided that relation I is observed, where d isthe average diameter defined as: p

:1 and d being the axes of the ellipse forming the major base, d and dbeing the axes of the ellipse forming the minor base, and d and d theaxes of the ellipse halfway between the bases. The antennae can haveauxiliary apparatus for adjusting the resonance frequency or impedance,or for reducing the dimensions without affecting the performance. Theauxiliary facilities, which are described below, are applied forsimplicity to the cylindrical antenna only, as shown in FIG. 2, but theycan of course also apply to the variant shown in FIG. 3.

According to a first auxiliary arrangement, shown in FIG. 4, a fixed orvariable capacitor 91 is connected at one end to a point 92 on theconductor acting as the antenna, and at the other end to ground 55.Independently or in combination, another capacitor 93 can be inserted inseries in conductor 51.

The capacitors can be used to adjust the resonance frequency of theantenna in its operating range.

FIG. 5 shows a second auxiliary facility. this time for driving theantenna by magnetic coupling. The central conductor of coaxial line 58is parallel to, but not connected to, conductor 51 for a length 101which can be adjustable and is connected to earth 55 at point 102. Thedistance between length 101 and conductor 51 can also be adjustable. Theantenna impedance can also be matched with the impedance of the coaxialline. FIG. shows telescopic separating members for keeping the requireddistance between wires 51 and 101.

FIG. 6 shows another auxiliary facility. The end 157 of conductor 51 isconnected to the center of a nonradiating roof Diameter of minor base ofcone: d

Arithmetical mean of diameters: d Numberofturns: N

Product: Nd

Height of truncated cone: h Resonance frequency: f Resonance wavelength:A Quotient: Nd/A Quotient: d/lt Quotient: h/k

Quotient: l/A

for a number of conical helical antennae constructed-according to theinvention.

TABLE II N 4.5 4.5 e 5.75 5.5 7.5 7.5 7.5 Nd 292 292 292 288 270 254 253209 203 h, 45 90 135 60 120 175 so 150 210 f,MHZ 131.5 129 129 132 129129 132.5 132.5 128 Mmn 2,300 2,300 2,300 2,300 2,300 2,300 2,300 2,3002,300 Na/x 0.127 0.127 0.127 0.125 0.120 0.115 0.114 0.114 0.114 (ti/M102. 33 2. s3 2. s3 2. 09 2. 09 2. 09 1. 52 1. 52 1. 52 (ll/D10 2 4 0 2.01 5.20 7.01 3.43 5.52 9.10 (l/x)10 3s 3s 3s 3s 3s 39 3s 3s 38 111consisting of radial conductors 112 and a circular conductor 113disposed in a plane parallel to ground level. The roof" enables theantenna to operate at a longer wavelength, if required, than in theabsence of a roof.

FIG. 7 shows a variant of the last-mentioned facility, in which the tooinstead of being a network of conductors, is a metal plate 121 connectedand disposed in the same manner as in FIG. 6.

FIG. 8 shows an advantageous method of constructing a roof having avariable area, which can be used to vary the resonance wavelength fromthe operating wavelength for a helical antenna without a roof to awavelength approximately 30 percent greater. The roof is made up ofindependent blades 121 which can rotate round a shaft 122 and are heldbetween abutments 123 and 124. The blades can open out like a fan. Thelower abutment 124 is connected to the end 157 of the helical antenna.If n is the number of blades, each blade can cover a sector of a circleover an are extending slightly more than 360/n. By opening and closingthe resulting fan, very large variations can be made in the capacitancebetween the antenna roof and earth level.

The following parameters are shown in Table l:

Diameter of helix: d

Number of turns: N

Product: Nd

Pitch of helix: p

Height of helix: h

Resonance frequency: f

Resonance wavelength:

Quotient: Nd/A Quotient: d/)t Quotient: h/k

Quotient: HA

These parameters are for a number of cylindrical helical antennaeconstructed according to the invention.

The tables show that: a. the quotient Nd/A in each case is between 0.10and 0. l4,

according to condition (1); b. the quantity I/)\ is always between 0.30and 0.45, according to condition (2), and c. if conditions l and (2) areobserved, the ratio d/k of the cylinder diameter or of the arithmeticalmeans of the end diameters of the truncated cone, to the wavelength, andthe ratio h/ of the height of the antenna to the wavelength, can bevaried within relatively wide limits with practically no adverse effecton performance. The limits are as followg 0.0l s dllt s 0.04 0.02 s h/As 0. I25

i.e. d must be between )1 I and )t /25 and h must be between )1 I50 andA 8.

As has been stated, the distance between the drive point and thegrounded end of the antenna is about one two-hundredths of thewavelength.

Up to now, the nature of the ground plane has been left undefined. Theground plane can, of course, be the metal wall of a vehicle or missile,etc.

A description will now be given of a particularly efficient andeconomical method of manufacturirg helical antennae according to theinvention: 1

Known helical antennae are made sufficiently rigid for operatingconditions, either through the intrinsic rigidity of the conductor ofwhich they are made, or by auxiliary elements such as masts, stays andbraces or by being wound round an insulating former. These elementscomplicate the structure, are unsightly, increase the weight and expenseof the antennae, and are difficult to manufacture, especially in amass-production process, when the antennae need to have smalldimensions.

One aim of the invention is to construct light, shapely anten- TAB LE ITable 11 gives the following parameters: Diameter of major base of cone:d,

nae which are extremely rigid and which have perfectly reproduciblecharacteristics.

Antennae manufactured by the method according to the invention cancomprise matching and adjusting elements such as roofs and variable orfixed capacitors, and can be embedded in a material such aspolymerisable resin, having a suitable color and external shape. so thatthe resulting appearance is suitable for each particular application.

According to the invention, a conical or cylindrical helical antenna ismanufactured by rolling a flexible sheet of a dielec tric, to whosesurface a thin metal conductor tightly adheres.

In the embodiment of a cylindrical antenna shown in FIGS. 10 and 11, aconducting strip 211 cut from a thin sheet of metal, e.g. copper, istightly glued or stuck by any other known method of manufacturingprinted circuits on to a rectangular sheet 210 of flexible dielectricmaterial such as laminated fibre glass and epoxy resin. The sheet 211 isthen rolled into a right cylinder. The resulting cylinder is held inposition by clamping, riveting, glueing or any other suitable method.

The dimensions of sides 212, 213, 214 and 215 of dielectric sheet 210,the length of conductor 211 and its slope 216 are chosen so that thecylinder obtained by rolling the sheet round an axis parallel to sides214 and 215 comprises a number of successive layers equal to the numberof turns in the helix being manufactured. In FIG. 11, for example, theantenna body comprises three layers of dielectric sheet 210, so thatconductor 211 forms a helix having three turns.

FIGS. 12 and 13, which correspond to FIGS. 10 and 11,

show a similar method of manufacturing a cylindrical helical antennahaving a number of matching and adjusting components.

Conductor 221 which is similar to conductor 211 is extended along partof sides 222 and 223 of dielectric sheet 220 by end bars 224 and 225,and has a connecting leg 226 extending perpendicularly towards bar 225.A terminal strip 227 is disposed near end bar 225.

Dielectric sheet 220 is rolled in the same manner as sheet 210 to givethe tubular antenna body shown in FIG. 13.

In FIG. 13, end bar 224 of conductor 221 is connected to a brassnonradiating component or roof 231 by a circular weld 232. End bar 225is similarly connected to a brass baseplate 233. The antenna is drivenby a coaxial line whose inner conductor 234 is connected, e.g. bywelding, to terminal strip 227, and the external conductor 235 isconnected to baseplate 233 by a connection 236.

Terminal strip 227 is connected to end bar 225 by a conductor 237.

An adjustable tuning capacitor 238 is connected between leg 226 andbaseplate 233.

FIG. 14 is a cross section of the antenna diagrammatically shown in FIG.13.

As FIG. 14 shows, the end bar 224 of conductor 221 is connected to brassroof 231 by circular weld 232, and end bar 225 is connected to baseplate233. Plate 233 is a solid brass disc provided with a circular groove 330for receiving the lower part of the tubular antenna body. Baseplate 233is fixed by locking or welding bar 225 in groove 330.

The opposite end of the baseplate is prolonged by a threaded shank 331for attaching the antenna to a support by tightening a nut 332. Threadedshank 331 is formed with a borehole 333 terminating in a device 334 forgripping and holding the coaxial line supplying power to the antenna.The inner conductor 234 of the coaxial cable is connected to terminalstrip 227, and the outer conductor 238 is connected to baseplate 233.

An opening 241 through the successive layers of dielectric sheet 220gives access to the component for adjusting the tuning capacitor 238disposed inside the antenna body. After being adjusted, the saidcomponent and the connection inside the antenna body can be held inposition by embedding them e.g. in a polymerisable resin 242.

In a variant shown in FIGS. 15a and 15b, parallel conductors 251 aredisposed on each side of a dielectric sheet 250. The conductors on eachsurface are, respectively, symmetrical with respect to the plane passingthrough the middle of the thickness of the dielectric.

The slope 254 of the conductors is such that, after the dielectric sheethas been rolled into a single turn, the ends of the conductors on onesurface overlap the ends of the conductors on the other surface so as toform the helix shown in FIG. 16. The conductors are connected by weldingat points 255.

Rectangular spare lengths 252, 253 without conductors are disposed ateach end of sheet 250 so as to hold the antenna body in position, e.g.by clamping or glueing.

FIGS. 17 and 18, which are similar in principle to FIGS. 10 and 11, showtwo essential stages in the manufacture of a conical helical antenna.FIG. 17 shows the unfolded surface of a truncated cone having a circularbase and made from a dielectric sheet 260 having a conductor 261 stuckto its surface. FIG. 18 shows the truncoconical antenna formed byrolling dielectric sheet 260 until the ends overlap.

The examples described are cylindrical or conical helical antennaehaving a circular base and a constant pitch. These embodiments, ofcourse, are in no way limitative and the cited method can be applied tothe manufacture of cylindrical or truncoconical helical antennae havinga noncircular, e.g. elliptical, base and/or a variable pitch. The citedextension of the process is an integral part of the invention.

More particularly, in the case of FIGS. 17 and 18 where, owing to itsnonrectilinear shape, the conductor cannot be manufactured in the formof a metal strip stuck to a sheet of dielectric material, part of thesurface of the sheet can be coated with metal, e.g. in the manner usedfor printed circuits.

We claim:

1. An antenna comprising a plurality of turns of a single conductorhelically wound around a geometrical surface having a longitudinal axis,one end of said conductor being connected to a conductive ground planeand its other end being free, said antenna comprising means for couplingit to a load circuit and being characterized in that, A denoting thewave length in free space corresponding to the operating frequency andby I the overall length of the wound conductor measured along saidconductor, A and l satisfy the relation:

0.3). s I s 0.45k

said coupling means including a short length of auxiliary conductorparallel and very near to, but not in contact with, said part of he saidantenna conductor and being coupled to said conductor along a partthereof close to and terminating on said ground place, the length ofsaid part being equal to a very small fraction of said wavelength, thesaid length of auxiliary conductor having one end connected to the saidground plane and the said load circuit being connected between the saidground plane and the other end of said length of auxiliary conductor.

2. An antenna according to claim 1, wherein an adjustable capacitor isconnected between one point on the conductor and the said ground plane.

3. An antenna according to claim 1, wherein the end of the conductorwhich is not connected to the ground plane is connected to a conductingelement acting as a capacitive load with respect to ground.

4. An antenna according to claim 3, wherein the conducting elementcomprises linear conductors disposed along the circumference and radiiof a circle.

5. An antenna according to claim 3, wherein the said element is a plane,metal conducting plate.

6. An antenna according to claim 3, wherein the said element comprises anumber of plates in the shape of sectors of a circle, which can berotated round a common axis.

7. An antenna according to claim 1, wherein said conductor consists of athin metal strip which adheres to a flexible sheet of dielectricmaterial rolled in the shape of said surface.

8. An antenna according to claim 7, wherein said conductor is a thinmetal strip printed on the surface of said dielectric sheet.

9. An antenna according to claim 7, wherein, it comprises auxiliarymatching elements held in position by immersion in a dielectricsubstance.

1. An antenna comprising a plurality of turns of a single conductorhelically wound around a geometrical surface having a longitudinal axis,one end of said conductor being connected to a conductive ground planeand its other end being free, said antenna comprising means for couplingit to a load circuit and being characterized in that, lambda denotingthe wave length in free space corresponding to the operating frequencyand by l the overall length of the wound conductor measured along saidconductor, lambda and l satisfy the relation: 0.3 lambda l 0.45 lambdasaid coupling means including a short length of auxiliary conductorparallel and very near to, but not in contact with, said part of thesaid antenna conductor and being coupled to said conductor along a partthereof close to and terminating on said ground place, the length ofsaid part being equal to a very small fraction of said wavelength, thesaid length of auxiliary conductor having one end connected to the saidground plane and the said load circuit being connected between the saidground plane and the other end of said length of auxiliary conductor. 2.An antenna according to claim 1, wherein an adjustable capacitor isconnected between one point on the conductor and the said ground plane.3. An antenna according to claim 1, wherein the end of the conductorwhich is not connected to the ground plane is connected to a conductingelement acting as a capacitive load with respect to ground.
 4. Anantenna according to claim 3, wherein the conducting element compriseslinear conductors disposed along the circumference and radii of acircle.
 5. An antenna according to claim 3, wherein the said element isa plane, metal conducting plate.
 6. An antenna according to claim 3,wherein the said element comprises a number of plates in the shape ofsectors of a circle, which can be rotated round a common axis.
 7. Anantenna according to claim 1, wherein said conductor consists of a thinmetal strip which adheres to a flexible sheet of dielectric materialrolled in the shape of said surface.
 8. An antenna according to claim 7,wherein said conductor is a thin metal strip printed on the surface ofsaid dielectric sheet.
 9. An antenna according to claim 7, wherein, itcomprises auxiliary matching elements held in position by immersion in adielectric substance.